With firefox themes enabled, when you hover over or click a toolbar button, the background of the button is from the OS theme and not the firefox theme.
Do you mean the background colours of the tooltips?
In the image link, if you look at the non-printing character icon, which is pressed, it doesnt have the firefox theme shown in it, it is showing the theme which would be there when there isnt any firefox theme applied.
You can see similar theme problems with the style, font name and font size drop downs.
Ok, but in this case it looks a little bit different in my case with LO 18.104.22.168 Win 8.1, because here they are blue and not grey. With blue selected buttons it is not that striking as with grey. But the drop-down list boxes are also grey. All in all, it would be nice if the buttons/boxes would fit good to the selected theme.
That is a limitation of the GTK+ 2 widget system, which has been in maintenance mode for quite a while. This issue does not happen in, e.g., Windows, where pressed buttons are semi-transparent. We don’t have the resources to create a toolkit à la Firefox (whose approach is to emulate everything and use .png and .svg assets for their custom widgets). With GTK+ 2 it is impossible to theme those buttons the way you want.
Thanks Adolfo for the insight. Just curious if this issue also affect gtk3?
It’s possible to fix this in GTK+ 3 themes.